Which process do protozoa use for ingestion?

Protozoa primarily utilize phagocytosis for ingestion, making this the correct answer. Phagocytosis is a specific form of endocytosis whereby the protozoan engulfs solid particles or other organisms. This process is essential for obtaining nutrients and involves the engulfing of food particles, which are then enclosed in a food vacuole. Within the food vacuole, the particles can be digested by enzymes.

In contrast, photosynthesis is a method used by certain organisms like plants and some algae to convert light energy into chemical energy, which is not applicable to the majority of protozoa that are heterotrophic and cannot perform photosynthesis. Osmosis, while crucial for maintaining water balance, refers to the movement of water across a semipermeable membrane rather than the uptake of nutrients. Absorption involves the uptake of soluble substances directly (such as nutrients) into the cell, but this is distinct from how protozoa typically ingest larger particles or organisms through phagocytosis. Thus, phagocytosis accurately describes the feeding mechanism employed by protozoa.